The present invention relates to network communication and initialization over an Ethernet local area network (LAN). More specifically the present invention relates to physical layer link signaling with shared autonegotiation.
Ethernet local area networks employ bidirectional communication between a local device such as a computer and its link partner to provide data sharing across the network. With such networks, it is important to provide compatibility to a wide array of devices which may potentially be connected to the network. Because such devices may have varying capabilities, it is necessary during initialization for both the local device and its link partner to exchange information regarding one another's capabilities in order to establish the most efficient common mode of communication. By providing such capability advertisement, various network interface devices may be used with each device operating at the most efficient common setting.
Autonegotiation is a function which provides the exchange of information between the local device and its link partner. A protocol for autonegotiation is specified in ANSI/IEEE Ethernet standard 802.3u-1995, at clause 28. The objective of the autonegotiation function is to provide the means to exchange information between two devices that share a link segment and to automatically configure both devices to take maximum advantage of their abilities.
The autonegotiation function allows the devices at both ends of the link segment to advertise abilities, acknowledge receipt and understanding of the common mode(s) of operation that both devices share, and to reject the use of operational modes that are not shared by both devices. Where more than one common mode exists between the two devices, a mechanism is provided to allow the devices to resolve to a single mode of operation using a predetermined priority resolution function. The autonegotiation function allows the devices to switch between the various operational modes in an ordered fashion; permits management to disable or enable the autonegotiation function; and allows management to select a specific operational mode.
The basic mechanism to achieve autonegotiation is to pass information encapsulated within a burst of closely spaced link integrity test pulses. This burst of pulses is referred to as a Fast Link Pulse (FLP) burst and includes a Link Code Word which identifies the abilities of the transmitting device. Each device capable of autonegotiation issues FLP bursts at power-up. The devices receiving the FLP bursts extract the Link Code Words from the FLP bursts to determine the communication modes supported by the transmitting devices (i.e. their link partners).
It is becoming more common to integrate four, eight or even sixteen Ethernet ports on a single integrated circuit, such as an Application Specific Integrated Circuit (ASIC). Currently, multi-port integrated circuits have dedicated autonegotiation controllers for controlling the autonegotiation function. Each autonegotiation controller services an individual port and requires about 9000 semiconductor devices or “gates”. Each gate requires a certain amount of physical space on the integrated circuit. Since space is limited on an integrated circuit, it is becoming more difficult to integrate higher numbers of ports in a single integrated circuit using the conventional approach.